Dr Evan Harris hardly fits the mould of cuddly Liberal Democrat MPs, who are usually so desperately anxious to be all things to all people.

Zealous, obsessive, and self-righteous, Harris, a former junior hospital doctor who now sits for the affluent Home Counties seat of Oxford West and Abingdon, has spent much of his Parliamentary career trumpeting his radical views on abortion, voluntary euthanasia, immigration and gay rights.

In the process, his fanaticism and lack of social grace has made him one of the most isolated MPs in the House of Commons, where he is viewed as a difficult loner.

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Though a few admire him for having the courage of his convictions, most of his colleagues across the political spectrum find him awkward and charmless, while his determination to enforce his hardline outlook on medical ethics has led to accusations of intolerance and manipulation of the political process.

Unmarried and without children, he has been nicknamed Dr Death around the corridors of Westminster because of his enthusiasm for abortion and voluntary euthanasia.

A Liberal Democrat MP for the past decade, Dr Harris was formerly his party's health spokesman, but today it is in his role as a member of the influential House of Commons Science and Technology Committee that he has been causing ferocious controversy, particularly on abortion.

It was Dr Harris who recently persuaded the Committee to review the 1967 Act which legalised abortion in this country where, today, an astonishing quarter of all pregnancies end in medical termination.

But instead of arguing for a tightening of the law, as much of the public wants in view of new evidence that foetuses can survive after just 20 weeks, Harris has called for greater liberalisation.

He also advocates an end to the requirement that any abortion requires the consent of two doctors, arguing that the procedure could easily be carried out by a nurse or even in the home by taking a pill.

The Health Service, he declares, must remove "false barriers to terminations".

Harris has been almost as controversial on the issue of voluntary euthanasia, where he has used his position as a member of the British Medical Association's Ethics Committee to push for the acceptance by the BMA of "assisted dying" for the terminally ill.

Many doctors, however, are unhappy about the way he carries on, claiming that he manipulates evidence and browbeats opponents.

Though of Jewish origin, he is an aggressive secularist, serving on the council of the National Secular Society and attacking anyone - particularly Christians - who allows their faith to influence their attitude towards abortion.

To Harris, radical political ideology is to be welcomed, but religion is not.

One telling moment occurred recently when he was in a debate on BBC Newsnight with the Tory MP Nadine Dorries, a former nurse who advocates reducing the abortion limit to 13 weeks.

Harris seemed to find her challenge intolerable.

At one stage, he claimed that the British abortion rate is no worse than anywhere else in Europe.

In reality, only the former Soviet state of Ukraine has a higher rate.

"He wants to ignore or distort the evidence to maintain his point of view. He's unbelievable," says Dorries.

Currently the Liberal Democrats' science spokesman, he has supported the use of human embryos in research and is a powerful defender of experimentation on animals, a particularly important local issue for him given that much of Oxford University - whose scientific faculties condone animal testing - lies in his constituency.

His stance on scientific issues does not impress everyone.

"He's just a self-publicist," argues Dr Ian Gibson, Labour MP and former chairman of the Commons Science and Technology Committee.

"What he knows about science could be put on the back of a postage stamp."

But there is a certain integrity about him. He bravely volunteered, for instance, to act as a guinea pig in trials of a new vaccine to combat the HIV virus.

And, as a self-described "extremist for freedom of speech", he led the successful campaign in Parliament last year against the Government's proposals to outlaw incitement to religious hatred, which he argued would create a new climate of censorship in Britain.

It is partly his tone of pious, ideological certainty that annoys his fellow MPs. Even the Liberal Democrats appear embarrassed about him.

After he had tried to crush a Conservative opponent, a northern Lib Dem said he was just "like a schoolboy politician" in his eagerness to score points.

Harris was first elected to Parliament in 1997 and initially, with his raven-haired, slim looks, capacity for hard work and natural eloquence, it appeared he might be destined for the top of the Liberal Democrats.

One MP said to me that, in his passion, articulacy and record of public service, there was a whiff of the young American senator Bobby Kennedy about Harris's first Parliamentary appearances.

But such high hopes were soon disappointed. Harris proved himself to be a near cardboard parody of a Leftwinger, still spouting the gospel of student days, demanding more immigration, a soft line on asylum seekers, greater taxation, higher public spending and more gay rights.

"He's way to the Left of us," commented a Labour MP.

Harris himself, at the last Lib Dem conference, said that he had taken up these views because his Oxford constituency is "full of gay atheist asylum seekers".

In his journey to the political extreme, Harris's appearance and behaviour has changed, growing ever more eccentric.

As he has slid away from the establishment, he has eschewed the suit in favour of a more proletarian jacket and odd trousers.

Fixated on his work, he is rarely seen around Westminster without the earpiece of a mobile phone.

Recently he had to attend the opening by the Queen of an Oxfordshire science centre. When he sat down at the top table with Her Majesty, the lead from the phone was still attached to his ear.

"Quite the oddest thing I have ever seen," says one fellow politician at the event.

Scurrying around his constituency or Westminster with sheaves of papers, he is perpetually late for meetings, sometimes failing to turn up. When he does show, he tends to bring a chill to proceedings with his earnestness and lack of humour.

Harris was born in 1965 in Sheffield, the son of an academic couple who, disillusioned with apartheid, had emigrated from South Africa.

His father Frank, a brilliant intellectual, went on to become a professor and dean of the medical faculty at Leicester University.

A bright child, Evan Harris was educated first at the Blue Coat school in Liverpool and then, as a scholarship winner, at Wadham College Oxford, studying medicine.

After graduating, he embarked on a career as a doctor working in hospitals in both Oxford and Liverpool, before becoming a public health official.

In 1994, still a young doctor, he was selected as the Liberal Democrat candidate for Oxford West.

Despite a strong majority, his career has never flourished at Westminster, even given the paucity of talent in the Liberal Democrat ranks.

In truth, he is seen as something of a nerd by his colleagues.

In Oxfordshire he lives like the eternal student bachelor, which has given rise to baseless rumours about his sexuality - not least because he is President of the Liberal Democrats Campaign for Lesbian and Gay Rights and vice-President of the Lesbian and Gay Humanist Association.

In fact, Harris has been married once, with the union ending in divorce in 1997.

He later had a tragically doomed relationship with an interior designer from Ireland, Liz O'Hara, who developed a malignant terminal brain tumour in 2003.

This harrowing experience led to his resignation as health spokesman from the Liberal Democrat frontbench so he could spend more time with her in her last months.

Harris's current girlfriend is the press manager for BPAS, formerly the British Pregnancy Advisory Service, one of the country's leading providers of abortion services.

In view of her job and his own loud advocacy for keeping the abortion time limit at 24 weeks, from which the BPAS benefits, Harris has felt the need to declare this relationship in advance of recent Parliamentary debates about abortion.

Yet to his opponents, this is just one further example of how closely tied he is to the abortion industry.

It is a strange irony that this man of supposed liberal compassion, the son of anti-apartheid èmigrès, should have ended up being known as Dr Death after a decade in Parliament.